1. Field of the Invention
The present invention relates to a piezo-electric device and an ink cartridge having the piezo-electric device, and more particularly to a piezo-electric device for liquid detection and an ink cartridge having the same.
2. Description of the Related Art
In an ink jet recorder, an ink jet recording head having a pressure generation means for pressurizing a pressure generation chamber and a nozzle opening for jetting pressurized ink as ink drops is mounted on a carriage.
The ink jet recorder is structured so as to continue printing by continuously feeding ink in an ink tank (ink container) to the recording head via a flow path. The ink tank is structured as a removable cartridge which can be simply exchanged by a user, for example, at the point of time when ink is consumed.
Conventionally, there are some management methods for ink consumption of the ink cartridge. One method is that the jet count of ink drops jetted by the recording head and the ink amount sucked in by maintenance are totalized by the software and the ink consumption is managed by calculation. The other method is that an electrode for liquid level detection is mounted on the ink cartridge, thereby managing the point of time when a predetermined amount of ink is actually consumed.
However, in the method for totalizing the jet count of ink drops and ink amount by the software and managing the ink consumption by calculation, the following problem is imposed. Some head has weight variations in injected ink drops. Weight variations in ink drops do not adversely affect the image quality. However, in consideration of a case of accumulation of errors in the ink consumption due to variations, the ink cartridge should be filled with a marginal amount of ink. Therefore, a problem arises that the marginal amount of ink remains in some cartridge.
On the other hand, the method for managing the point of time of consumption of ink by an electrode can detect the actual amount of ink. Therefore, the ink residue can be managed highly reliably. However, the detection of the ink level depends on the conductivity of ink, so that the kind of detectable ink is limited and the seal structure for the electrode is complicated. Further, as a material of the electrode, a noble metal which is highly conductive and anticorrosive is generally used, so that the manufacturing cost of the ink cartridge is increased. Furthermore, since two electrodes must be mounted, the manufacturing processes are increased, and as a result, the manufacturing cost is increased.
To solve the aforementioned problem, in Japanese Patent Application No. 2000-147052, a piezo-electric device which can accurately detect the liquid residue, requires no complicated seal structure, and is mounted in a liquid container is described.
According to the art relating to the aforementioned patent application, by use of changing of the resonance frequency of a residual vibration signal generated due to the residual vibration of the vibration part of the piezo-electric device in a case of existence of ink in the space opposite to the vibration part of the piezo-electric device and a case of non-existence of ink, the ink residue in the ink cartridge can be monitored.
FIGS. 19 and 20 are drawings showing a piezo-electric device of the related art. The piezo-electric device has a base 200 structured so as to laminate a diaphragm 202 on a substrate 201, and a cavity 203 for receiving a medium to be detected is formed on the base 200. At both ends of the base 200, a lower electrode terminal 204 and an upper electrode terminal 205 are formed. Furthermore, in the central part of the base 200, a lower electrode layer 206 connected to the lower electrode terminal 204 is formed, and a piezo-electric layer 207 is laminated on the lower electrode layer 206, and an upper electrode layer 208 is laminated on the piezo-electric layer 207.
Further, on the base 200, an auxiliary electrode layer 209 is formed, and the auxiliary electrode layer 209 electrically connects the upper electrode layer 208 and the upper electrode terminal 205, and a part thereof is positioned between the diaphragm 202 and the piezo-electric layer 207 and supports an extension part 210 of the piezo-electric layer 207 from underneath. Since the extension part 210 of the piezo-electric layer 207 is supported by the auxiliary electrode layer 209 like this, the extension part 210 is prevented from producing a stepwise part.
Further, as clearly shown in FIG. 20, the auxiliary electrode layer 209 is formed so as to be positioned outside the region corresponding to the cavity 203. The reason is that since the diaphragm 202 in the region corresponding to the cavity 203 and the piezo-electric layer 207 constitute the vibration part of the piezo-electric device, the auxiliary electrode layer 209 is formed outside the region of the vibration part, thus the vibration characteristic of the piezo-electric device is prevented from deterioration.
However, in the aforementioned conventional piezo-electric device, when the piezo-electric device is driven and the vibration part is vibrated, a problem arises that at the position of the arrow A shown in FIG. 20, cracks are easily generated on the piezo-electric layer 207 and the upper electrode layer 208.
The cause of generation of cracks is considered as indicated below. Namely, as shown in FIG. 20, between the lower electrode layer 206 and the auxiliary electrode layer 209, a gap 211 for ensuring an insulating state between the two is formed and the gap 211 is formed so as to include the position corresponding to a periphery 203a of the cavity 203. Therefore, when the vibration part of the piezo-electric device is vibrated by driving the piezo-electric device, stress concentration is generated on the piezo-electric layer 207 at the position corresponding to the periphery 203a of the cavity 203 and this is considered to cause generation of cracks.
Further, as clearly shown in FIG. 19, in the conventional piezo-electric device, in the region corresponding to the cavity 203, the piezo-electric layer 207, the lower electrode layer 206, and the upper electrode layer 208 constituting the vibration part are formed in an asymmetrical shape as a whole. Therefore, a problem arises that the weight balance in the vibration part of the piezo-electric device gets worse and the vibration characteristic of the vibration part is deteriorated.
The present invention was developed with the foregoing in view and is intended to provide a piezo-electric device for preventing a generation of cracks in a piezo-electric layer and improving a vibration characteristic of a vibration part of the piezo-electric device.